1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for gating a dedicated physical control channel signal to increase a user data transmission capacity.
2. Description of the Related Art
The applicant has proposed a technique for gating a dedicated physical control channel signal to 3GPP (3rd Generation Partnership Project) for standardization of UMTS (Universal Mobile Terrestrial System), which is a next generation mobile communication system. The dedicated physical control channel signal gating technique proposed by the applicant is a technique for gating a dedicated physical control channel signal if there is no data to transmit over a dedicated data channel established between a UTRAN (UMTS Terrestrial Access Network) and a UE (User Equipment) for a predefined time. Unlike the proposed technique for gating the dedicated physical control channel signal, the present invention relates to an apparatus and method for gating a dedicated physical control channel signal in a downlink physical shared channel/dedicated physical channel (DSCH/DCH) state where a UTRAN transmits data to a plurality of UEs over downlink physical shared channels and transmits control data and physical channel control signals over downlink dedicated physical channels, and the UEs then transmit control data and physical channel control signals over uplink dedicated physical channels.
First, a description will be made of a channel structure of an asynchronous UMTS (Universal Mobile Terrestrial System) mobile communication system.
The UMTS channels are classified into physical channels, transport channels and logical channels. A downlink channel of the physical channels is divided into a physical downlink shared channel (PDSCH) and a downlink dedicated physical channel (DPCH). The downlink dedicated physical channel is divided into a downlink dedicated physical control channel (DPCCH) and a downlink dedicated physical data channel (DPDCH). The downlink dedicated physical data channel DPDCH and the downlink dedicated physical control channel DPCCH are time-multiplexed within one slot and orthogonal-despread with associated orthogonal codes to be separated from other physical channels, and then spread with a unique scrambling code for the UTRAN before transmission. An uplink channel of the physical channels includes a dedicated physical channel (DPCH), which is divided into an uplink dedicated physical control channel (DPCCH) and an uplink dedicated physical data channel (DPDCH). The uplink dedicated physical data channel DPDCH and the uplink dedicated physical control channel DPCCH are orthogonal-spread with associated orthogonal codes to be separated from each other, and then summed up and spread with one scrambling code before transmission. A structure of the downlink dedicated physical channel will be described with reference to FIG. 1.
FIG. 1 illustrates a structure of a downlink dedicated physical channel for a mobile communication system. One frame of the downlink dedicated physical channel is comprised of 15 slots Slot#0-Slot#14, and each slot is comprised of a dedicated physical data channel DPDCH for transmitting upper layer data from a UTRAN to a UE, and a dedicated physical control channel DPCCH which includes a TPC (Transmit Power Control) symbol for controlling a physical layer control signal, i.e., transmission power of the UE, a TFCI (Transport Format Combination Indicator) symbol, and a Pilot symbol. As shown in FIG. 1, each slot of the dedicated physical channel is comprised of 2560 chips. A first data symbol Data1 and a second data symbol Data2 indicate the upper layer data transmitted from the UTRAN to the UE through the dedicated physical data channel DPDCH, and the TPC symbol indicates information for controlling transmission power of the UE, transmitted from the UTRAN to the UE. The TFCI symbol indicates with which TFC (Transport Format Combination) the downlink channel transmitted for the currently transmitted one frame (10 ms) has been transmitted, and the Pilot symbol provides a criterion based on which the UTRAN can control transmission power of the dedicated physical channel. Here, information included in the TFCI can be classified into a dynamic part and a semi-static part: the dynamic part includes transport block size information and transport block set size information, while the semi-static part includes information on TTI (Transmission Time Interval), channel coding method, coding rate, static rate matching and CRC size. Therefore, the TFCI indicates the number of transport blocks of the channel transmitted for one frame, and the TFCs that can be used at each transport block, to which numbers are assigned.
Next, a structure of the uplink dedicated physical channel will be described with reference to FIG. 2.
FIG. 2 illustrates a structure of an uplink dedicated physical channel for a mobile communication system. Like the downlink dedicated physical channel, one frame of the uplink dedicated physical channel is comprised of 15 slots Slot#0-Slot#14. Each slot of the dedicated physical data channel DPDCH of the uplink dedicated physical channel transmits the upper layer data from the UE to the UTRAN, and has the following format. That is, the slot is comprised of a Pilot symbol used as a channel estimation signal when the UE demodulates data to transmit to the UTRAN, a TFCI symbol indicating with which TFC the channels transmitted for the currently transmitted frame will transmit data, an FBI (FeedBack Information) symbol for transmitting feedback information when a transmission diversity technique is applied, and a TPC symbol for controlling transmission power of the downlink channel.
A process for controlling transmission power of the uplink dedicated physical channel and the downlink dedicated physical channel will be described hereinbelow.
First, a description will be made of a process for controlling transmission power of the uplink dedicated physical control channel and the uplink dedicated physical data channel. After defining the TPC=00 symbol value of the downlink dedicated physical channel as a power-up command to increase transmission power of the uplink dedicated physical control channel and the uplink dedicated physical data channel and further defining the TPC=11 symbol value of the downlink dedicated physical channel as a power-down command to decrease transmission power of the uplink dedicated physical control channel and the uplink dedicated physical data channel, the UTRAN controls transmission power of the dedicated physical control channel and the dedicated physical data channel of the UE, i.e., the uplink dedicated physical control channel and the uplink dedicated physical data channel, using the TPC symbol of the downlink dedicated physical channel. Whether to increase or decrease the transmission power of the uplink dedicated physical control channel and the uplink dedicated physical data channel is determined by the UTRAN depending on signal strength of a pilot symbol of the uplink dedicated physical control channel received from the UE. When the signal strength of the pilot symbol is higher than or equal to a predefined value, the UTRAN transmits a power-down command to the UE through the TPC symbol; in contrast, when the signal strength of the pilot symbol is lower than the predefined value, the UTRAN transmits a power-up command to the UE through the TPC symbol, thereby enabling the UE to transmit the uplink dedicated physical control channel and the uplink dedicated physical data channel at proper transmission power.
Second, a description will be made of a process for controlling transmission power of the downlink dedicated physical channel. After defining the TPC=00 symbol value of the uplink dedicated physical control channel as a power-up command to increase transmission power of the downlink dedicated physical channel and further defining the TPC=11 symbol value of the uplink dedicated physical control channel as a power-down command to decrease transmission power of the downlink dedicated physical channel, the UE controls transmission power of the downlink dedicated physical channel using the TPC symbol of the uplink dedicated physical control channel. Whether to increase or decrease the transmission power of the downlink dedicated physical channel from the UTRAN is determined by the UE depending on signal strength of a pilot symbol of the downlink dedicated physical channel received from the UTRAN. When the signal strength of the pilot symbol of the downlink dedicated physical channel is higher than or equal to a predefined value, the UE transmits a power-down command to decrease transmission power of the downlink dedicated physical channel through the TPC symbol of the uplink dedicated physical control channel; otherwise, when the signal strength of the pilot symbol of the received downlink dedicated physical channel is lower than the predefined value, the UE transmits a power-up command to increase transmission power of the downlink dedicated physical channel through the TPC symbol of the uplink dedicated physical control channel, thereby enabling the UTRAN to transmit the downlink dedicated physical channel at proper transmission power.
Next, a structure of the downlink physical shared channel will be described with reference to FIG. 3.
FIG. 3 illustrates a structure of a downlink physical shared channel for a mobile communication system. One frame of the downlink physical shared channel is comprised of 15 slots Slot#0-Slot#14. A chip rate of the UMTS system is 2.84 Mcps. The 15 slots each have 2560 chips, and transmit the upper layer data to the UE in association with the dedicated physical channel for designation of the TPC and the TFCI. The downlink physical shared channel is a channel for efficiently transmitting a large amount of packet data to the respective UEs, and is shared by a plurality of UEs. In order for the UEs to use the downlink physical shared channel, a separate dedicated physical channel must be maintained between the UEs and the UTRAN. That is, a downlink dedicated physical channel and an uplink dedicated physical channel, interlinked with the downlink physical shared channel, must be maintained between the UEs and the UTRAN. Since the downlink physical shared channel is shared by a plurality of UEs, the utilization efficiency of the downlink physical shared channel increases with the number of UEs sharing the downlink physical shared channel. That is, since the downlink physical shared channel is shared by a plurality of UEs, a certain UE must individually set up the downlink and uplink dedicated physical channels in order to use the downlink physical shared channel. For example, if N UEs share the downlink physical shared channel, the UEs each set up one downlink dedicated physical channel and one uplink dedicated physical channel, so that the N UEs use the N downlink dedicated physical channel and the N uplink dedicated physical channels. The downlink physical shared channel is a channel physically set to transmit a large amount of packet data, while the dedicated physical channel is a channel physically set to transmit a small amount of packet data and retransmission-related data, compared with the downlink physical shared channel.
As stated above, when the UE is provided with a packet data service, the downlink physical shared channel and the downlink dedicated physical channel are interlinked with each other, and this will be described with reference to FIGS. 4 and 5.
FIG. 4 illustrates a structure of a TFCI of a dedicated physical channel in a mobile communication system. As illustrated in FIG. 4, a TFCIDPCH symbol transmitted over the downlink dedicated physical channel is information indicating a transport format of the downlink physical shared channel. The downlink TFCI symbol indicates to which UE the packet data transmitted over the downlink physical shared channel is to be transmitted after a lapse of a predetermined time, and the UE can determine whether exists downlink physical shared channel data to be received, by constantly analyzing the downlink dedicated physical channel received. When the TFCI symbol received by the UE indicates that there exists data to be received by the UE on the downlink physical shared channel of the next frame, the UE must receive the downlink physical shared channel data at the frame. Hence, the UE receives the data transmitted by the UTRAN by demodulating and decoding the signal received over the downlink physical shared channel at the frame transmitted to the UE itself. In addition, the TFCI of the downlink physical shared channel is used to determine proper transmission power of the data transmitted over the downlink physical shared channel, and the UTRAN determines transmission power of the downlink physical shared channel on the basis of the proper transmission power of the downlink physical shared channel. With reference to FIG. 5, a description will be made of transmission power of the downlink physical shared channel and the downlink dedicated physical channel and structures thereof, when the downlink physical shared channel and the downlink dedicated physical channel are interlinked with each other as stated above, i.e., in the downlink shared channel/dedicated physical channel (DSCH/DCH) state.
FIG. 5 illustrates an interlinking scheme of a downlink physical shared channel and a downlink dedicated physical channel in a mobile communication system. As illustrated in FIG. 5, data communication in the normal downlink shared channel/dedicated physical channel (DSCH/DCH) state is proper for a service in which a UE has a short time for actually receiving data over the downlink physical shared channel (DSCH) and has a relatively long waiting time. In FIG. 5, the downlink shared channel is assumed to be a downlink physical shared channel, and the dedicated channel is assumed to be a dedicated physical channel. In the DSCH/DCH state, in order to maintain a proper channel state through power control for a waiting time, the UE performing data communication must transmit and receive a downlink dedicated channel DCH (i.e., a downlink dedicated physical channel signal) interlinked with the downlink shared channel, i.e., the downlink physical shared channel, and an uplink dedicated channel DCH (i.e., an uplink dedicated physical channel signal). As stated above, in order to maintain the downlink physical shared channel, the UE must continuously transmit and receive the downlink and uplink dedicated physical channel signals, causing battery consumption and an increase in interference to both the downlink and the uplink. As a result, the number of the UEs sharing the downlink physical shared channel is limited.
In addition, in the case of the downlink physical shared channel, the UEs time-divide the downlink physical shared channel after assigning radio resources to the downlink physical shared channel, and for efficient radio resource assignment to the downlink physical shared channel, it is important for a resource manager to have the downlink physical shared channel be always used. However, a generated amount and a generation time of data to be transmitted from the UTRAN to the UEs are irregular and unexpectable, so that it is not possible to constantly transmit data over the downlink physical shared channel.
Therefore, in order to increase efficiency of the downlink physical shared channel, it is necessary to increase the number of UEs sharing the downlink physical shared channel. That is, the increase in number of UEs using the downlink physical shared channel increases a probability that data will be transmitted over the downlink physical shared channel for a predetermined time, thereby resulting in an increase in utilization efficiency of the downlink physical shared channel. However, in order to increase the number of UEs sharing the downlink physical shared channel, it is necessary to set up the dedicated physical channels interlinked with the downlink physical shared channel for the respective UEs, so that the radio resources for setting up and maintaining the dedicated physical channels are required. Accordingly, the number of the dedicated physical channels, which can be simultaneously set up, is limited.